CHEM 205

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CHEM 205 Tutorial 0
chapter 1
http//www.karentimberlake.com/chemodul.htm
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• Units of measurement

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Measurement

• You are making a measurement when you
• Check you weight
• Read your watch
• Take your temperature
• Weigh an apple

What kinds of measurements did you make today?
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Some Tools for Measurement

How do you measure. Temperature? Time? Volume? We
ight?
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Measurement in Science

• In Science we
• do experiments
• measure quantities
• use numbers to report measurements

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Units in the Metric System (S.I.)

• length meter m
• volume liter L
• mass gram g
• temperature Celsius C

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Stating a Measurement

• In every measurement there is a

NUMBER followed by a UNIT from measuring device
The patients temperature is 102F. The sack
holds 5 lbs of potatoes. It is 8 miles from your
house to school. The bottle holds 2 L of orange
soda
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• Significant Figures

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Reading a measure

• First digit (known) 2 2.?? cm
• Second digit (known) 0.7 2.7? cm
• Third digit (estimated) between 0.05- 0.07
• Length reported 2.74 cm
• or 2.75 cm
• or 2.73 cm

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Known, significant, estimated digits

• 2.74 cm

Significant!
Known (100 certain)
Estimated (uncertain)
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What is the length of the line?

• l5. . . . I . . . . I6. . . .I . . . . I7. .
  cm
• 1) 6.0 cm
• 2) 6.06 cm
• 3) 6.60 cm

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Exact Numbers

• Obtained when you count objects
• 2 soccer balls
• 1 watch
• 3 pizzas
• Obtained from a defined relationship
• 1 foot 12 inches
• 1 meters 100 cm
• Not obtained with measuring tools

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Classify each of the following as an exact (E) or
a measured (M) number.

• A._M_Gold melts at 1064C
• B._E_1 yard 3 feet
• C._M_A red blood cell with diameter 6 x 10-4 cm
• D._E_There were 6 hats on the shelf
• E._M_A can of soda contains 355 mL of soda

A.___Gold melts at 1064C B.___1 yard 3
feet C.___A red blood cell with diameter 6 x
10-4 cm D.___There were 6 hats on the
shelf E.___A can of soda contains 355 mL of soda
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• Significant Figures in Calculations

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Counting Significant Figures

• Number of Significant Figures
• 38.15 cm
• 0.008 ft
• 25000 in
• 0.48600 gal

4 1 2 5
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Significant Numbers in Calculations

• A calculated answer cannot be more precise than
  the measuring tool.
• Significant figures are needed for final answers
  from
• 1) adding or subtracting
• 2) multiplying or dividing

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Adding and Subtracting

• The answer has the same number of decimal places
  as the measurement with the fewest decimal
  places.
• 25.2 ONE decimal place
• 1.34 TWO decimal places
• 26.54
• answer 26.5 ONE decimal place

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• In each calculation, round the answer to the
  correct number of significant figures.
• A. 235.05 19.6 2.1
• 1) 256.75 2) 256.8 3) 257
• B. 58.925 - 18.2
• 1) 40.725 2) 40.73 3) 40.7

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Multiplying and Dividing

• Round (or add zeros) to the calculated answer
  until you have the same number of significant
  figures as the measurement with the fewest
  significant figures.

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In each calculation, round the answer to the
correct number of significant figures.

• A. 2.19 X 4.2
• 1) 9 2) 9.2 3) 9.198
• B. 4.311 0.07
• 1) 61.58 2) 62 3) 60
• C. 2.54 X 0.0028
• 0.0105 X 0.060
• 1) 11.3 2) 11 3) 0.041

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• Prefixes and
• Equalities

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Metric Prefixes

• Increase or decrease basic unit by 10
• Form new units larger or smaller than the basic
  units
• 0.00356 3.56 x 10-3
• 123 000 000 000 000 123 x 1012

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Prefix Symbol Value Exponential
giga G 1,000,000,000 109
mega M 1,000,000 106
kilo k 1,000 103
hecto h 100 102
deca da 10 101
no prefix means no prefix means 1 100
deci d 0.1 10-1
centi c 0.01 10-2
milli m 0.001 10-3
micro m 0.000001 10-6
nano n 0.000000001 10-9

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Give the value of the following units

• A. 1 kg ____ g
• 1) 10 g 2) 100 g 3) 1000 g
• B. 1 mm ____ m
• 1) 0.001 m 2) 0.01 m 3) 0.1 m

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Equalities

• State the same measurement in two
• different units
• length
• 10.0 in.
• 25.4 cm

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Conversion Factors

• Express an equality between two different units
• Example 1 in 2.54 cm
• Factors 1 in and 2.54 cm
• 2.54 cm 1 in

3 in ? ? cm
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3 in x
7.62 cm
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Blood has a density of 0.05 g/mL. If a person
lost 0.30 pints of blood at 18C, how many ounces
of blood would that be?

• Initial unit pints Final unit

oz
1 US pint 16 US fluid ounces
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How many seconds are in 14 days?
14 day x 1 day x 60 min x 60 s
24 h 1 h
1 min
14 day x 24 h x 60 min x 60 s
1 day 1 h 1 min
1.2 x 105 s
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Steps to solve a problem

• READ problem
• IDENTIFY data
• Write down a unit plan
• from the INITIAL UNIT to the DESIRED UNIT
• Select CONVERSION factors
• Change initial unit to desired unit
• CANCEL units and check
• Do math on CALCULATOR (is the result
  logical?)
• Give an answer using SIGNIFICANT FIGURES

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• Measuring Temperature

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Kelvin Scale

• 0 K is the lowest temperature
• 0 K - 273C
• K C
• K C 273

C K - 273
37C to K? K C 273 37C 273
310 K
298K to C ? C K - 273 298 - 273
25 C
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• Density

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Density
Density compares the mass of an object to its
volume
Note 1 mL 1 cm3
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What is the density (g/cm3) of 48 g of a metal if
the metal raises the level of water in a
graduated cylinder from 25 mL to 33 mL?

• 1) 0.2 g/ cm3 2) 6 g/cm3 3) 252
  g/cm3

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What is the density (g/cm3) of 48 g of a metal if
the metal raises the level of water in a
graduated cylinder from 25 mL to 33 mL?

• Volume (mL) of water displaced
• 33 mL - 25 mL 8 mL
• Volume of metal (cm3)
• 8 mL x 1 cm3 8 cm3
• 1 mL
• Density of metal
• mass 48 g 6 g/cm3
• volume 8 cm3
• Solution 6 g/cm3 (2)

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Which diagram represents the liquid layers in the
cylinder? (K) Karo syrup (1.4 g/mL) (V) vegetable
oil (0.91 g/mL) (W) water (1.0 g/mL)
W
V
V
W
V
W
1
2
3
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Density as Conversion Factor

• A substance has a density of 3.8 g/mL.
• Density 3.8 g/mL
• Equality 3.8 g 1 mL 1 cm3
• Conversion factors

38
The density of octane, a component of gasoline,
is 0.702 g/mL. What is the mass, in kg, of 875
mL of octane?

• 1) 0.614 kg
• 2) 614 kg
• 3) 1.25 kg

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The density of octane, a component of gasoline,
is 0.702 g/mL. What is the mass, in kg, of 875
mL of octane?

• Unit plan mL ? g ? kg
• Equalities 1 mL 0.702 g and 1 kg 1000
  g
• Calculation
• 875 mL x 0.702 g x 1 kg
  0.614 kg
• 1 mL 1000 g
• Solution 0.614 kg (1)